1. Field of the Invention
The invention relates to multiple spindle bar machines and, more particularly, to a multiple spindle bar machine especially suitable for manufacturing small lot sizes. The machine permits quick tool changeovers, has short cycle times, and can be operated substantially automatically.
2. Description of the Prior Art
Conventional bar machines are mechanically based, that is, they rely on complex gear trains to control the operation of spindles and other parts. Such machines are expensive to manufacture, require highly skilled personnel to operate, have long setup times, and run at relatively slow operating speeds. These machines are suitable for long manufacturing runs. It is difficult to manufacture complex parts because only a few machining operations can be performed on a given machine. In many cases the parts must be removed from one machine and installed on another machine in order to complete all machining operations.
In recent years, the versatility of bar machines has been enhanced by the introduction of computer numeric control (CNC). Also, synchronous motors have been used to drive spindles and spindle slides, thereby increasing the capabilities of the machines. Many of the machines in question advance bar stock along a single axis (the Z axis). Typically, these machines advance the stock through a main spindle toward a counterspindle that is coaxial with the main spindle. Machining operations are performed on the front of the stock by turret-mounted tools in a work station located between the opposing main spindle and counterspindle. After the workpiece has been grasped by the counterspindle while the counterspindle is rotating at the same speed as the main spindle, the workpiece is severed from the remainder of the stock and withdrawn by the counterspindle. Additional machining operations then can be performed on the back of the workpiece. Examples of such single axis machines are U.S. Pat. No. 4,457,193 to Matthey, U.S. Pat. No. 4,719,676 to Sansone, U.S. Pat. No. 4,949,444 to Kojima et al;, U.S. Pat. No. 5,152,201 to Izawa, and U.S. Pat. No. 5,471,900 to Corwin et al.
Enhanced variations of these machines are known. For example, the Izawa patent also discloses a multi-axis machine in which a workpiece is advanced along the Z axis, but it also can be moved along the X axis (horizontally of the machine). This result is accomplished by mounting the counterspindle on slides that can move along both the X axis and the Z axis. As used herein, the term xe2x80x9cZ axisxe2x80x9d refers to any axis the same as or parallel to an axis about which workpieces are rotated, including the longitudinal centerline of the machine. The term xe2x80x9cX axisxe2x80x9d refers to any axis that extends radially from the Z axis and which is perpendicular to the Z axis.
U.S. Pat. No. 5,207,134 to Wakatsuki discloses a single-axis machine in which two counterspindles are disposed side-by-side. The counterspindles can be moved along both the X axis and the Z axis. This construction enables each counterspindle to grasp the workpiece at different stages in the machining process.
U.S. Re. Pat. No. 33,252 to Link et al. discloses a machine in which a turret-mounted counterspindle is movable along the X and Z axes. The turret itself is rotatable about the X axis. A third tool carrier is disposed away from the main spindle and offset from the Z axis. With this machine, a workpiece grasped by the counterspindle can be pivoted away from the main spindle and moved laterally to the third tool carrier for performing machining operations on the back of the workpiece.
U.S. Pat. No. 5,207,135 to K. Babuder et al. discloses a machine having drum-mounted multiple main spindles. A single counterspindle is aligned with a selected one of the main spindles. Upon indexing the drum, the main spindles will be moved from station to station about the Z axis. Workpieces held by the main spindles thus can be indexed about the Z axis to sequential workstations where machining operations can be performed on the front of the workpieces by turret-mounted tools that slide along the X axis. After various machining operations have been performed on a given workpiece, the workpiece can be grasped by the counterspindle, severed from the stock, and withdrawn along the Z axis so that machining operations can be performed on the back of the workpiece by slide-mounted tools that move along the X axis.
Despite the advances of recent machines such as those referenced, there remains a need for a bar machine that can manufacture small lot sizes, has a quick tool changeover time, has very short cycle times, and which can be operated substantially automatically.
In response to the foregoing concerns, the present invention provides a new and improved multiple spindle bar machine. In the preferred embodiment, the machine according to the invention features three main spindles that are opposed by three counterspindles of substantially identical construction. The region between an opposed main spindle and a counterspindle is referred to as a workstation. The main spindles can be indexed about the Z axis. The counterspindles cannot be indexed, but they can move back and forth along the Z axis. A workpiece-grasping collet chuck is mounted to the end of each main spindle, and preferably to each counterspindle as well. The main spindles are rotated in unison while the counterspindles are rotated independently. All of the spindles are driven by computer-controlled motors.
In the preferred embodiment, three tool-carrying turrets that index about the Z axis are radially spaced around the machine at the workstations. Preferably, the turrets located at the first and second workstations can be moved along both the X and Z axes, while the turret located at the third workstation can be moved along the X axis. A slide-mounted cutoff that moves along the X axis is located at the third workstation. The invention includes a clamp for maintaining the main spindles in a desired indexed position and a tri-lobal toolslide that supports the counterspindles for movement.
The foregoing construction makes the machine exceedingly versatile. For example, one or more of the counterspindles can be fitted with drill bits or counterbores. Because the main spindles and the counterspindles are independently controlled, the effective rotational speed of a bit or counterbore can be doubled if the main spindle and the counterspindle are rotated in opposite directions. Typically, drilling and turning operations will be performed at the first workstation. End face machining and counterboring will be performed at the second workstation. At the third workstation, the workpiece will be severed from the stock by the cutoff after the spindles have been synchronized and the front of the workpiece has been grasped by the counterspindle. Thereafter, additional machining operations such as center drilling and thread rolling can be performed on the back of the workpiece by tools carried by the third turret.
Because the spindles are hollow, long workpieces can be accommodated by the counterspindles. If desired, workpieces can be passed from the main spindles to the corresponding counterspindles and back again to the main spindles. This feature is useful where it is desirable to perform machining operations on the back of a workpiece before performing operations on the front of the workpiece. The particular toolslide used with the invention provides good support for the counterspindles while permitting them to be positioned closely together.
The foregoing and other features and advantages of the invention will be apparent to those skilled in the art after a review of the accompanying specification, claims, and drawings.